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SPECIAL BRONZES

237

hydrochloric acid and the phosphoric acid precipitated in the usual way
(see Determination of Phosphorus in Iron in presence of Arsenic).

2. Determination of Tin, Copper, Zinc, etc.桽ee Ordinary Bronzes.1

*

* *

In some bronzes for bushes, pistons, etc., subject to attrition, quantities of
phosphorus varying from 0-25 to 2-5% are sometimes present with a view to
obtaining quite special effects. In ordinary phosphor-bronzes smaller quan-
tities are found (less than 0-25%).

Silicon -bronzes

These are used especially for telegraph and telephone wires, as they
have high electrical conductivity and resistance to tension. Their analysis
includes :

1.  Determination of Silicon.𦌽0 grams of the sample, according
to the supposed silicon content, are treated with aqua regia (3 parts of
hydrochloric acid and I part of nitric acid), the solution being evaporated
to dryness, the residue taken up twice with about 15 c.c,. of concentrated
hydrochloric acid and evaporated, and the residue heated in an oven at
135 to render the silica completely insoluble.   The residue is treated with
hydrochloric acid, the subsequent procedure being as in the determination
of silicon in iron.    In the present case also the purity of the silica must be
investigated by treatment with sulphuric and hydrofluoric acids.

2.  Determination of the Tin, Iron, Zinc, Nickel,  Phosphorus,
Sulphur, etc.桝s with ordinary bronzes2 (q.v.).

Silicon-bronzes, besides a little tin and often a little zinc, contain very small
quantities of silicon (0-05-1%) introduced in the form of silicon-copper as a
deoxidiser. According to Hampe the best bronzes for telegraph and telephone
wires have the following percentage compositions :

TABLE  XXIV
Compositions of Silicon-bronzes

For telephone wires
For telegraph wires

Cu

97-12
99-94

Sn
1-14
0-03

Si

0-05
0-03

Fe

trace
trace

Zn

I-12

Lead-bronzes

Lead-bronzes, also called American bronzes owing to their widespread
use in America, besides copper and tin contain considerable quantities of
lead and sometimes phosphorus, and are used for bearings and parts of
machines subject to friction, the lead increasing largely the plasticity of the
alloy. Their analysis includes :

1. Determination of the Tin, Lead, Copper, Iron, Zinc, etc.

1 The presence of phosphorus in the metastannic acid separating to be borne in mind.
8 The presence Of silica in the metastannic acid separating to be borne in mind.ions of the usual constituents